On the Mechanism of the Reactivity of 1,3-Dialkylimidazolium Salts under Basic to Acidic Conditions: A Combined Kinetic and Computational Study.

Comprehensive spectroscopic kinetic studies illustrate an alternative mechanism for the traditional free-carbene intermediated H/D exchange reaction of 1,3-dialkylimidazolium salts under neutral (D O) and acidic conditions (DCl/D O 35 wt % solution). The deuteration of high purity [bmim]Cl in D O is studied at different temperatures, in absence of catalyst or impurities, to yield an activation energy. DFT transition-state modelling, of a small water cluster and [bmim] cation, also yields an activation energy which strongly supports the proposed mechanism.

Capricious selectivity in electrophilic deuteration of methylenedioxy substituted aromatic compounds.

Ring deuteration via the SEAr mechanism, which is usually problem-free, is found to be troublesome with methylenedioxy substituent aromatics. We report a case where the deuteration not only partially fails at one of the ortho positions but also is completely prevented by a conformation dependent effect at the other o-position. Such selectivity discrepancies are important due to the widespread occurrence of methylenedioxy substituted natural products.

Stereochemistry and rearrangement reactions of hydroxylignanolactones.

Various conflicting data on the rearrangement and absolute stereochemistry of hydroxylignano-9,7'-lactones are resolved using 18O labeled compounds, also confirmed by an X-ray analysis of a pure lignano-9,7'-lactone enantiomer, obtained for the first time. Under NaH/DMF rearrangement conditions a silyl protected hydroxylignano-9,9'-lactone underwent an unexpected silyl migration.

Autoxidation of conjugated linoleic acid methyl ester in the presence of alpha-tocopherol: the hydroperoxide pathway.

Autoxidation of conjugated linoleic acid (CLA) methyl ester follows at least partly Farmer's hydroperoxide theory. A mechanism for this hydroperoxide pathway has been proposed based on autoxidation of 9-cis,11-trans-CLA methyl ester. This investigation aims at confirming and further clarifying the mechanism by analyzing the hydroperoxides produced from 10-trans,12-cis-CLA methyl ester and by theoretical calculations.

NMR properties of conjugated linoleic acid (CLA) methyl ester hydroperoxides.

NMR data on lipid hydroperoxides is scarce. In this study, hydroperoxides were produced from methyl 9-cis,11-trans-octadecadienoate and from methyl 10-trans,12-cis-octadecadienoate by autoxidation in the presence of 20% of alpha-tocopherol. Ten different hydroperoxides were isolated from the autoxidation mixtures of the two conjugated linoleic acid (CLA) methyl esters by SPE and HPLC.

Asymmetric synthesis, stereochemistry and rearrangement reactions of naturally occurring 7'-hydroxylignano-9,9'-lactones.

The asymmetric synthesis of a series of (7'S,8R,8'R)-7'-hydroxylignano-9,9'-lactones is presented, among them the mammalian lignan (7'S)-hydroxyenterolactone and (7'S)-parabenzlactone, allowing the stereochemistry of natural occurring (-)-parabenzlactone to be re-assigned. A hydroxylactone rearrangement and its possible mechanisms are discussed. Finally a brief survey of the current naming and numbering variants of 7'-hydroxylignano-9,9'-lactones is presented, along with a suggestion for harmonization of the nomenclature.

Stereochemistry of the hydroperoxides formed during autoxidation of CLA methyl ester in the presence of alpha-tocopherol.

The initial steps in the autoxidation of CLA methyl ester are poorly understood. The aim of this study was to determine the stereochemistry of the hydroperoxides formed during autoxidation of CLA methyl ester in the presence of a good hydrogen atom donor. For this purpose, 9-cis,11-trans CLA methyl ester was autoxidized in the presence of alpha-tocopherol under atmospheric oxygen at 40 degrees C in the dark.